It is a well-known fact that there are magnetic recording media having a multiple layer structure, rather than a single layer structure, for matching with each recording wavelength band.
Also, multiple layered magnetic recording media having a nonmagnetic layer as a lower layer are described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 187418/1988 and 191315/1988, which aim at improving the electromagnetic transferring property.
A magnetic recording media of multiple layer structure having a magnetic layer as a lower layer tends to have shorter recording wavelength with the increase in recording density. Other problems include layer thickness loss in recording and reproduction due to output reduction etc. when the magnetic layer is thick. To cope with this drawback, it is common practice to reduce the thickness of the upper magnetic layer. However, when upper layer thickness is reduced, the upper layer surface is susceptible to the dispersibility and surface condition of the lower layer, tending to result in a deteriorated electromagnetic transferring property. Another problem is that the lower magnetic layer becomes hard and brittle, resulting in increased magnetic flocculation, which can deteriorate surface smoothness.
Although a magnetic recording medium having a nonmagnetic layer as a lower layer surpasses a magnetic recording medium having a magnetic layer as a lower layer in surface smoothness and electromagnetic transferring property, lower layer coatability is poor due to poor properties of magnetic coating compound, such as low elasticity. The upper layer is therefore susceptible to the lower layer and has poor coatability. Another drawback is difficulty in layer thickness uniformization, which in turn cause a drawback of low productivity.
The lower nonmagnetic layer is also problematic that it is likely to have a high friction coefficient because of surface smoothness, resulting in a deteriorated running property and durability.
Also, when the nonmagnetic powder incorporated in the lower layer has a low true specific gravity, poor dispersibility of coating compound results in surface roughness upon coating, which in turn deteriorates the electromagnetic transferring property.
Another problem is that it is difficult to produce a magnetic recording medium having an excellent electric property and running property for a control signal due to a lack of control output because the lower layer is a nonmagnetic layer.